Surface temperature indicator light for ceramic top infrared radiant range

ABSTRACT

A control panel indicator light arrangement for an infrared cooking range surface unit having a resistance element supported on a heater block underlying an infrared transmissive, translucent cover plate. A double-throw thermostatic switch, having terminals alternatively connected to an auxiliary heater and the indicator light, is supported in heat transfer relation with the heater block by a heat-conducting bracket embedded in the block such that the auxiliary heater is energized with the resistance element to actuate the thermostatic switch at a predetermined temperature allowing the auxiliary heater to initially hold the indicator light circuit closed. After a time interval the thermostatic switch continues to hold the indicator light circuit closed by means of the conductive flow of heat from the heater block to the switch via the bracket such that the arrangement provides visual indication on the control panel of the cover plate temperature condition.

United States Patent [72] Inventor Homer W. Deaton Centerville, Ohio[21] Appl. No. 55,816 [22] Filed July 17, 1970 [45] Patented Oct. 12,1971 [73] Assignee General Motors Corporation Detroit, Mich.

[54] SURFACE TEMPERATURE INDICATOR LIGHT FOR CERAMIC TOP INFRAREDRADIANT RANGE 7 Claims, 7 Drawing Figs.

52 US. Cl 219/453, 219/449, 219/461, 219/463, 219/464, 219/506, 219/553,338/280 [51] Int. Cl 1105b 3/68 [50] Field of Search 219/451-452,

[56] References Cited UNITED STATES PATENTS 600,057 3/1898 Ball 338/2802,450,399 9/1948 Schiedler 219/453 2,870,316 1 1959 Fergusom lr. 219/453Primary Examiner-- Volodymyr Y. Mayewsky Attorneys-William S. Pettigrew,Frederick M. Ritchie and Edward P. Barthel ABSTRACT: A control panelindicator light arrangement for an infrared cooking range surface unithaving a resistance element supported on a heater block underlying aninfrared transmissive, translucent cover plate. A double-throwthermostatic switch, having terminals alternatively connected to anauxiliary heater and the indicator light, is supported in heat transferrelation with the heater block by a heat-conducting bracket embedded inthe block such that the auxiliary heater is energized with theresistance element to actuate the thermostatic switch at a predeterminedtemperature allowing the auxiliary heater to initially hold theindicator light circuit closed. After a time interval the thermostaticswitch continues to hold the indicator light circuit closed by means ofthe conductive flow of heat from the heater block to the switch via thebracket such that the arrangement provides visual indication on thecontrol panel of the cover plate temperature condition.

PATENTEDD 12 ml 3, s 1 2 826 SHEET 1 BF 3 I PATENTEDUET 12 ml SHEET 2 OF3 A TTORNEY PATENTEU 2 3,812,826

SHEET 3 BF 3 INVIjN'I'OR,

A TTORNE) SURFACE TEMPERATURE INDICATOR LIGHT FOR CERAMIC TOP INFRAREDRADIANT RANGE The present invention relates to ceramic top infraredradiant ranges having a cooking surface provided by a glassceramicinfrared transmissive cover plate and more particularly to anarrangement for indicating the temperature condition of the cover plate.

With the advent of glass-ceramic cover plates for domestic ranges of thetype having infrared radiant heaters a need has arisen to sense thetemperature of the infrared transmissive cover plate to indicate to theoperator the temperature condition thereoflThis is of particularimportance in radiant-type cooking units whose resistance element isspaced from the undersurface of a translucent ceramic cover plate suchthat the resistance element is not visible to the operator. Adescription of a preferred heating unit for use with the presentinvention is found in the commonly assigned copending US. Pat.application, Ser. No. 48,390, filed June 22, 1970.

In the particular embodiment of this invention a plurality of radiantcooking units are covered by a utensil-supporting cover plate ofmilky-appearing glass-ceramic material having one or more heating areasthereon. When the infrared radiant units are on and raised to a minimumtemperature, depending upon the lighting conditions of the kitchen, adull orange glow will appear on the cover plate heating area portion ofthe surface indicating that the electrical resistance element of theunit below the heating area is energized. Because the unit may be set ata low or simmer temperature below such minimum temperature or due to anintense lighting condition in the kitchen there is not always a visualindication that the cover plate heating area is hot. In addition, whenthe heating unit is turned off the resistance element ceases to glow andthe glassceramic material returns to its milky color, with the resultthat such a light coloring may appear cool to the operator when in factthe cover plate retains residual heat above a safeto-touch temperaturefor varying lengths of time.

Accordingly, it is an object of this invention to provide asurface-temperature-indicating device for an infrared radiant cookingunit having an air-exposed or open coil-type resistance element spacedbelow an infrared transmissive glassceramic cover plate.

Another object of the present invention is to provide an inexpensivesurface-temperature-indicating device for the control panel of a ceramictop range having infrared radiant cooking units which will not interferewith the transmission of infrared energy from resistance elements spacedbelow the infrared transmissive glass-ceramic cover plate.

It is another object of this invention to provide asurfacetemperature-indicating device for a ceramic top range having aplurality of infrared radiant cooking units underlying an infraredtransmissive cover plate formed of translucent glassceramic materialwherein a control panel indicating light informs the operator of thetemperature condition of the ceramic cover plate.

These and other objects and advantages will become apparent from thefollowing description, reference being had to the accompanying drawingswherein a preferred embodiment of the invention is clearly shown. In thedrawings:

FIG. 1 is a fragmentary perspective view of a domestic range with partsbroken away;

FIG. 2 is an enlarged vertical section taken along the line 2-2 in FIG.1;

FIG. 3 is an enlarged vertical section taken along the line 33 in FIG.1;

FIG. 4 is an enlarged view in top elevation of one of the heatingassemblies removed from the range;

FIG. 5 is a partial elevational view of the assembly illustrated in FIG.4;

FIG. 6 is a vertical section taken along the line 6--6 of FIG. 5; and

FIG. 7 is a schematic diagram for a range circuit incorporating theinvention.

Referring now to the drawings, in FIG. I, domestic range 10 isillustrated having metal body 11 supporting an upper casing 12 whichincludes a collar 14 around the top edge thereof forming a top opening16 located above upper insulation retainer wall 17 of the range body. Asseen in FIG. 2 the top opening is defined by a continuous dependingflange 18 located therearound while the collar 14 merges with the rearwardly located control panel 19 having a plurality of control knobs 20thereon for selectively energizing infrared radiant heating units asdescribed.

A pair of heating assemblies generally indicated at 22, 23 in FIG. 1 areespecially adapted to be installed in spaced side-byside relationship inthe upper casing 12 of the range and located in spaced relation abovethe upper wall 17 of the range body. As seen in FIG. 4 the heatingassemblies are generally rectangular in shape for location below theopening 16 with each assembly having its longitudinal axis orientedparallel to the sides of the range. As the heating assemblies 22, 23 areidentical in construction and are reversible to occupy either theleft-hand or the right-hand operative position shown in FIG. 1 likereference characters are used to designate like or corresponding partsthroughout the several views with the exception that the left-handassembly 23 has its reference characters primed on the drawing. Withinthe top opening 16 (FIG. 2) is an upper utensil-supporting glass-ceramiccover plate 24 that defines the complete surface cooking area of therange 10. The cover plate 24 extends throughout the planar extent of theopening 16 and has a continuous planar undersurface 25 that contacts theupper faces of the underlying heating units positioned within theassemblies 22, 23 in a manner to be described.

It should be noted that while the heating assemblies 22, 23 aredescribed in conjunction with a free-standing range it is to beunderstood that the present invention is not intended to be so limitedand the assemblies could be used for example with a ceramic top kitchencounter cooking arrangement without departing from the scope of theinvention. Furthermore, the invention contemplates a single heatingassembly being used with a cover plate in a range or kitchen counterproviding two cooking areas or a single cooking area.

The utensil-supporting cover plate 24 is preferably formed of a highstrength infrared transmissive material such as recrystallizedglass-ceramic sold under the trade name Cer-vit by Owens-Illinois orI-Iercuvit by Pittsburgh Plate Glass. It will be appreciated howeverthat other infrared transmissive material, such as high-silica glass,for example, could be used with the invention without departing from thescope thereof. The cover plate 24 is shown in a preferred embodimenthaving a rectangular configuration with a length of approximately 25inches, a width of approximately 20 inches and a thickness of the orderof one-quarter inch providing a smooth top cooking surface that willaccommodate four radiant heating areas in a manner similar to aconventional electric range having four convolute-shaped conductionsurface heating units.

Turning now to FIGS. 2, 3 and 4 the heating assemblies 22, 23 each havea housing or pan member generally indicated at 26 formed from lightgauge sheet metal blanks comprising a bottom wall 27 providedwith'marginal sidewalls 28, 29 and end walls 30, 31 upstanding from thebottom wall. Each end wall 30, 31 terminates in a substantiallyhorizontal end flange wall 32, 33 outstanding from the top of the endwalls 30, 3I respectively and having downwardly directed lip portionsrepresented at 34' in FIG. 3.

As indicated above the cover plate 24 together with the underlyingheating or cooking assemblies 22, 23 are mounted in the opening 16substantially flush with the upper surface of the collar 14 by securingmeans including a trim ring indicated generally at 40 together with aplurality of cooperating clips 41 having individual pressure screws 42.As best seen in FIG. 3, the trim ring 40 is substantially T-shaped incross section and includes a head 43 spanning gap 44 formed between therange collar 14 and the longitudinal and transverse edges of the coverplate 24, together with a depending stem 45 disposed in the gap. A stem45 has formed along its lower ends hook portion 46 which providesshoulder means for interlocking engagement with a cooperating hookportion 47 on the clip member 41.

The clips 41 are dispersed at spaced intervals around the cover plate toengage the underside of the range collar 14 by seating circular beadportion 48 of the clips in the radiused area formed by the dependingflange 18 of the opening, whereupon the clip pressure screws 42 aretaken up to retain the plate and the heating assemblies in the opening.Pressure screws 42 have rectangular plate members 49 located on the endsthereof for pressure contact with the underside of the flange walls 32,33 when the pressure screws are taken up. The result is the housings 26together with the cover plate 24 are anchored to the range collar 14 ina manner to hold cooking or heating units to be described in pressurecontact with the undersurface of the cover plate.

Cover plate cushion members formed of fibrous insulating materials suchas asbestos pads 50 are provided between the underside of the coverplate and the upper surfaces of the end flange 32, 33. Appropriatesealing material, located between the inner and outer strips of the trimring head 43 and the underlying perimeteral borders of the cover plate24 and collar 14 provide a liquid-type seal therebetween. This material,such as manufactured by Dow Corning under the trade name RTV Silicone,cures to form a high-temperature rubberlike seal to prevent spillage oneither the cover plate or the range collar from entering the gap 44.

It will be noted that the heating assemblies 22, 23 are secured to therange collar 14 and cover plate 24 by housing flange walls 32, 33 onlyalong the longitudinal edges 51 of the cover plate. As seen in FIG. 2,the borders adjacent transverse edges 52 of the plate 24 are retained tothe range collar 14 by means of the trim ring and clip assemblydescribed. Annular washer-type pressure members 54 are used on thepressure screws 42 along the transverse cover plate edges 52. The uppersurfaces of the washer member 54 have resilient cushioning pads thereonformed from suitable material such as heat-resistant silicone rubber.

In the illustrated form of the invention each housing 26 provides aboxlike receptacle defined by its side, end and bottom walls forreceiving a resilient insulation mat 60 formed from suitable inorganicfibers insulation material such as rock wool, glass wool, asbestosfibers or the like. The mat 60 in the preferred embodiment has athickness of approximately 1 inch and a density of approximately 6pounds per cubic foot. As indicated in the plan view of FIG. 4 the mat60 extends throughout the bottom of the housings 26 conforming to theshape of bottom wall 27. It will be noted that in the disclosed form ofthe housing 26 there is an oblique wall portion 56 forming part of thesidewall 28 to accommodate a smallersized heating unit to be described.

FIG. 4 shows a plan view of the right-hand heating assembly 22 removedfrom the range 10. As explained earlier the heat- .ing assembly 22 maybe reversed end-for-end for insertion in the left-hand portion of therange top. Insulation mat 60 in the housing 26 has located thereon apair of cooking units indicated at 61, 62. Each of the units 61, 62comprises a heater support block and a heater resistance element withthe cooking unit 61 having its heater block shown at 63 supporting aribbon shaped-in-cross section resistance element 64 while the unit 62has a heater block 65 supporting a similar shaped resistance element 66.In the form shown the continuous ribbon element 64 is located within aconvolute-shaped groove 67 defining an annular heater area approximately8 inches in diameter while the continuous ribbon element 66 is locatedwithin a convolute-shaped groove 68 to define a heater areaapproximately 6 inches in diameter. The heater blocks are preferablymade of a fibrous ceramic refractory material having minimal thermalconductivity and low thermal mass, as discussed in detail in theaforementioned copending patent application, Ser. No. 48,390, andcomposed mainly of silica and alumina.

In the case of the right-hand cooking assembly 22 it is shown orientedwith the larger cooking unit 61 at the front of the range while theleft-hand assembly 23 has been reversed to locate the smaller cookingunit at the front of the range top. In this way the cooking assemblies22, 23 are able to provide alternate small and large surfaced heatingareas at both the front and rear of cover plate to provide maximum spacefor cooking utensils. It will be observed that the larger heater block63 has a generally octagon shape when viewed in FIG. 4 locating three ofits sides respectively adjacent to and substantially parallel with theend wall 30 and sidewalls 28, 29 of the housing 26. The smaller or6-inch-heater block has an irregular shape in plan to conform to theoblique wall portion 56 of the housing along with the housing walls 29and 31.

As seen in FIG. 3 representing the heater block 63' for the left-handassembly both the blocks 63, 65 have an overall thickness which whencombined with the thickness of the supporting mat 60 locates their upperperipheral faces 69, 70 respectively, a defined distance above thehousing flange walls 32, 33 such that the peripheral faces 69, 70 arebrought in flush heat transfer contact with the undersurface 25 of thecover plate. The faces 69, 70 of the heater blocks are held in cushionedpressure abutment with the cover plate by means of the trim ring 40 andclip 41 arrangement previously described.

The heater blocks 63, 65 are retained in the housing 26 prior to finalassembly by means of holddown pins whose heads are shown at 72 in FIG.4. Each holddown pin extends through a central bore in the heater blockstogether with aligned bores in the mat 60 and housing outer wall 27 forreception on the free end of the pin of a suitable retaining member suchas a push nut (not shown). A complete description of the heating unitmounting device may be found in copending application, Ser. No. 55,815,filed July 17, 1970 and assigned to the same assignee of thisapplication.

The heater blocks 63, 65 are cast or molded to provide diskshapedhollows defining recessed substantially circular areas 80, 81 (FIG. 4)in the block upper faces 69, 70 respectively. In the preferred form, theblocks 63, 65 have substantially identical thicknesses, within castingtolerances, of approximately 1.25 inches. For the purpose of thisdisclosure the heater blocks differ only in their outer configurationand size of their recessed areas with the blocks 63, 65 having theirrecessed areas indicated at and 81 to provide different sized heatingareas for the cover plate. Accordingly, only the larger cooking unit 61need be discussed in detail with all remarks being applicable to thesmaller unit 63 with the single exception that unit 63 has a lowerwattage output. It will be observed that the blocks 63, 65 are formedwith opposed cavities indicated at 78, 79 (FIGS. 4, 5 and 6)respectively to receive one end of a central heat-sensing deviceindicated generally at 82 cooperating with a surface temperatureindicating light circuit to form the subject matter of the presentinvention, the detailed description of which follows.

It should be mentioned that each of the cooking units has a temperaturecontrol means generally indicated at 83, 84 in FIG. 4 for the right-handcooking assembly shown. The control means 83, 84 are part of a coverplate temperature cutofi' control device to ensure that the temperatureof the cover plate does not exceed a maximum upper limit. The controlmeans 83, 84 form no part of the instant invention and are described inUS. Pat. application, Ser. No. 74,399 filed Sept. 22, 1970, alsoassigned to the assignee of the present invention.

Considering now the cooking units 61, 61' of FIGS. 2, 3 and 4 it will beseen that the convolute groove 67 provides a path for locating thecontinuous resistance element ribbon 64 such that one end is positionedfor electrical connection to an inner terminal member and its oppositeend located for connection to an outer terminal member 91. The terminalmembers 90, 91 are identical so as to be interchangeable with eithercooking unit and comprise an insulating column 92 formed of electricalporcelain or the like provided with an axial chamber receiving avertical terminal blade 93 therein as shown in the section view in FIG.2. The details of the terminal connectors form no part of the instantinvention and are described and claimed in the copending application,Ser. No. 55,815 filed July 17, 1970, assigned to the assignee of theinstant invention.

By virtue of the foregoing description it will be noted that theresistance element 64, which has a deeply undulating or sinelikepattern, is supported in the spiral groove 67 to establish a definedvertical airgap indicated at G in FIG. 3 between the cover plateundersurface 25 and the element which in the fonn shown provides aminimum spacing therebetween on the order of V4 inch. The A-inch gap Gis the minimum distance permitted by Underwriters Laboratory between anuninsulated conducting member and adjacent conductor.

To produce the required wattage output for the cooking units it wasdetermined that a resistance element be used that can be self-heated inthe range of 1,500 P. to 2,000 F. and constructed of a high-temperatureresistance material from the iron-chromium-aluminum family. Aniron-chromium-aluminum ferrite alloy is preferred because it has ahigher melting point and a higher electrical resistivity allowing it tobe operated at higher temperatures within the above-mentioned range. Forfurther details of the resistance element together with arrangement forbeing supported on the heater block reference should be had to thecopending application, Ser. No. 48,390, referred to previously.

Turning now to the instant invention, as noted previously of the heaterblocks 63, 65 are formed to receive a portion of the centralheat-sensing device 82 which is centrally located in the housing 26 in agap between the spaced blocks. As best seen in FIGS. 5 and 6 the sensingdevice 82 comprises a heat-sensing or heat-conducting bracket member 150having a pair of aligned channel-shaped end members 154 and 156, formedintegral with a central horizontal bracket or bridge plate 158. Thechannel members 154, 156 are supported on the insulation mat 60 which isprovided with a central hole 159 for reception of the lower portion ofthe heat-sensing device 82 while the bottom wall 27 of the housing hasan opening 161 for passage of suitable electrical leads to be described.In the form shown the bracket is formed from sheet steel having athickness of approximately 0.043 inches.

The bracket plate 158 has a pair of horizontally extending coplanarflanges 162 and 163 formed below the plane of the plate 158 by suitabledepending elements 164, 165. A thermostatic switch assembly 166 ismounted on the horizontal flanges 162, 163 by suitable means such as theroundhead screws 168, 170 shown threaded in holes in the horizontalflanges 162, 163. Extending upwardly from the outer ends of the flanges162, 163 are a pair of vertical leg members 172, 174 having horizontalfoot portions 176, 178 extending outwardly therefrom providing stopswhich serve only for engaging the undersurface 25 of the cover plateduring inverted assembly of the cooking assemblies with the range uppercasing 12. As seen in FIG. 6 the foot portions 176, 178 are spaced fromthe cover plate when the assembly is in its normal righted condition anddo not provide a direct heat path from the cover plate. An auxiliary oranticipator heater 180 preferably of the porcelain type having a wattagerating of the order of 200 watts at 1 18 volts, such as manufactured bythe Hotwatt Company for example, is located on the underside of thecentral bracket plate 158 so as to be interposed between and in thermalcontact with the upper end of thermostatic switch 166 and the overlyingbracket plate 158.

The thermostatic switch 166 in the preferred embodiment is a single-poledouble-throw heat changeover switch of the exposed bimetal-disk-typeproviding snap-action, such as manufactured by Texas Instruments lnc.under the trademark Klixon for example. The thermostatic switch 166 hasa tubular casing including an open bimetal disk end defined by a flangedannular rim 182 that is detachably secured tothe bracket flanges 162,163 by the means recited to position the disk in juxtaposition to theauxiliary heater 180. The thermostatic switch 166 is of the widedifferential type calibrated to trip during an ascending heat cycle whena temperature of the order of 170 F. is attained and to trip at atemperature of the order of 120 F. in a descending heat cycle.

F 16. 6 shows the opposed channel-shaped end members 154 and 156 of thebracket 150 extending into the cavities 78,

79 respectively, where upon tightening of the pressure screws 42 ofclips 41 the brackets are pressured between the mat 60 and the heaterblocks 63, 65. In this way the brackets are effectively embedded orburied in the heater blocks such that the entire outer surface of thechannel members 154, 156 are in heat exchange contact or relationshipwith their associated heater block members for a purpose to beexplained. As best seen in FIG. 5 porcelain insulator block members areprovided at 184 and 186 conforming with the channel portions of thebracket and extend outwardly therefrom complementary with the curvedinner ends of the cavities 78 and 79 to fill the voids of the bracketchannels 154, 156. It will be noted that the porcelain blocks 184, 186serve as insulators to reduce heat radiation from the bracket to providean efficient heat transfer path between the heater blocks 63, 65 and thethermostatic switch 166.

Turning now to the circuit arrangement of FIG. 7 power is supplied tothe range top from the usual single-phase, 236- volt, alternatingcurrent, three-wire Edison service entrance found in an adequately wiredresidence. The three wires are identified as line wires L, and L, and aneutral wire N it being understood that there is a potential of about236 volts across lines L, and L and about 1 18 volts across either lineL, or L and the neutral wire N.

Since the right-hand and left-hand heating assemblies are identical theyare shown in the circuit diagram with the same elements identified withthe same reference numerals, the exception being that each referencenumeral for the left-hand assembly is primed. For example, the heatingassembly 22 has a thermal switch 166 while the same thermal switch inheating assembly 23 is identified as 166. The line L, is connected toenergy-pulsing infinite heat switch assemblies 190 and 190', shown boxedin by dashed lines, by means of conductor 193 while the line N connectsenergy-pulsing infinite heat switches, indicated similarly at 192, 192',by means of conductor 194.

The infinite heat switches 190, 190' and 192, 192' are of a conventionaltype more particularly set forth in U.S. Pat. No. 2,623,137 issued Dec.23, 1952, and except for different wattage ratings are identical. Theinfinite heat switch 190 includes a first single-pole single-throw lineswitch (SPST) for the cooking unit 61 having a pair of contactsindicated at 195, 196 and a second single-pole single-throw switch for asignal lamp circuit having pair of contacts 197, 198. As its associatedcontrol knob 20 is rotated from its ofi position both the first line andsecond signal lamp SPST switches close by a cam (not shown) to routepower to the unit 61 and to light signal lamp 199.

As line L, is connected by conductors 200 and 201 to line contact 198 ofinfinite heat switch 190 it will be seen that the continuous resistanceelements 64 of the 8-inch cooking unit 61 is placed across a 236-voltagesource. The infinite heat switch 190 functions in the same manner toenergize the resistance element 64' across line L,, L, to provide 236volts of power producing a wattage output from elements 64, 64' varyingfrom zero to approximately 2,000 watts.

The infinite heat switch 192 has a first single-pole singlethrow lineswitch for the 6-inch cooking unit 62 providing a pair of contacts 202,203 and a second single-pole singlethrow switch for the signal lampcircuit having a pair of contacts 204, 205. Again, as the associatedcontrol knob 20 of infinite heat switch 192 is rotated from its offposition both these first and second SPST switches close to route powerto the resistance wire 66 and to light the signal lamp 199. As the lineN is shown connected by conductor 194 to the infinite heat switch 192while line contact 203 is connected to L, by conductor 200 it will beseen that the continuous resistance element 66 of the 6-inch cookingunit 62 is placed across a l 18- volt source to energize the element 66to produce a wattage output therefrom varying from zero to approximately1,200 watts.

More particularly, as shown in the power circuit of FIG. 7, the devicefor indicating the surface temperature condition of the cover plate 24is illustrated as including a conductor 206 electrically connected tothe contact-carrying arm 208 of the infinite heat switch 192. The arm208 has a cam and cam follower arrangement (not shown) that is rotatableto cause movement of the contact 210 on the arm 208 with respect to acontact 212 on the electrically conductive bimetallic arm 214 of theswitch which has one end thereof fixedly connected to a suitable supportmeans with respect to which the contact-carrying end of the bimetallicarm 214 is free to deflect. The infinite heat switch 192 furtherincludes a heater 216 that is connected electrically to the arm 214 andby a conductor 218 to one end of the ribbon resistance element 66 of theright-hand 6-inch unit 62. The opposite end of the resistance element 66is connected by means of a normally closed thermal heat limit switch 220to a conductor 222 which is in turn connected electrically to thecontact 202 of the infinite heat switch. The surface pilot light 199 isconnected to line L of the power source through the closed contacts 204,205, conductors 224, 225 thence through the lamp 199 to a conductor 226electrically connected to the conductor 194 of the neutral power sourceN.

To complete the description of the circuit the conductor 193 from line Lis electrically connected by conductor 227 to contact carrying arm 228of the infinite heat switch 190. The arm 228 has contact 230 for pulsingcontact with a contact 232 on the electrically conductive bimetallic arm234 of the switch, and further includes a heater 236 electricallyconnected to the arm 234 by a conductor 238 to one end of the resistanceelement 64 of the right-hand 8-inch unit 61. The opposite end ofresistance element 64 is connected by thermal heat limit switch 235 to aconductor 237 which leads to contact 195 of the line switch. Both thethermal switches 220 and 235 are part of the control means 84, 83respectively mentioned above as the subject of copending patentapplication, Ser. No. 74,399. The closed contacts 197, 198 energize thepilot light 199 through conductor 239.

As shown in FIG. 7 the lower contact 240 of the switch portion ofthermostat 166 is connected by the conductor 242 to the auxiliary heater180 while the other side of the heater 180 is connected by the conductor244 to the contact 195 of the infinite heat switch 190 of unit 61. Theheater 180 is also connected by conductor 246 to the contact 202 of theinfinite heat switch 192 of unit 62. In this manner the auxiliary heater180, mounted on the bracket 150, is connected across lines L and Nwhenever either one or both of the pair of line contacts 195, 196 or202, 203 of the infinite heat switches are closed and with thebimetallic disk 247 of the thermostatic switch 166 in its lower positionin engagement with contact 240. A suitable indicator light 250 islocated on the range control panel 19 so as to illuminate a glass lens251 having an appropriate indicator such as l-lot Surface" etchedthereon. The indicator light 250 is connected in the power circuit so asto be energized whenever the upper contact 252 of the disk 247 is closedacross lines L and N by lead 255 to conductor 193 and lead 254 toconductor 194, respectively.

It will be appreciated that the metal bracket 150, which in the instantembodiment is formed from sheet steel material having a thickness ofabout 40 mils, serves as a heat conductor or heat path between thefibrous-ceramic heater blocks 63, 65 and the thermostatic heatchangeover switch 166 to render its bimetallic disk subject to theconductive heat of either or both of the heater blocks. The refractoryfibrous-ceramic heater blocks 63, 65 absorb heat by virtue of being indirect contact with the energized resistance elements 64, 66 such thatheat is conducted from the elements downwardly into the blocks at thesame time that infrared rays are directed upwardly through the coverplate.

While some heat is also conducted into the blocks 63, 65 because theirupper faces 69, 70 are in pressure thermal contact with the undersurface25 of the cover plate it is to be noted that this source is minimal andby far the bulk of heat transfer to the blocks is by direct conductionfrom the resistance element. As there is an initial thermal lag ortemperature differential between the rise in temperature of the heaterblocks 63, 65 and the temperature ascent of the cover plate 24 it is notpossible for the blocks to initially serve as an analog of the coverplate temperature. This characteristic produces a time delay of variablelength during which the heating or cooking areas of cover plate 24achieve an elevated temperature of at least approximately F., atemperature standard above which an object is considered too hot totouch by most individuals.

As stated earlier because of their milky or cloudy condition certaininfrared transmissive optically opaque materials, such as translucentglass-ceramic for example used in the instant embodiment for the coverplate 24, there may be no visual indication from the resistance elementthat a heating area on the cover plate 24 is hot at temperatures of theplatebelow approximately 500 in indirect lighting or higher temperaturesin strong direct lighting. When the resistance element is deenergized itquickly loses its characteristic orange glow so that without applicantsindicating device no warning of the possible residual heat property ofthe cover plate exists.

By virtue of the auxiliary heater 180 being simultaneously energizedwhen either one of the resistance elements 64, 66 is energized theenergy generated by the auxiliary heater 180 supplies initial heat tothe thermostat switch 166 to cause the temperature of its bimetallicdisk 247 to lead or anticipate the heater block temperature. When thethermostatic disk 247 reaches a preselected temperature of approximately170 F. which in the instant case involves a time interval of the orderof 20 seconds, the thennal switch 166 is actuated turning on theindicator light 250 and turning off the auxiliary heater 180. Theauxiliary heater 180, which has an output of 200 watts at 118 volts inthe disclosed form, causes the temperature of the heated bracket tocontinue to rise for a period of overshoot because of the residual heatof the heater 180.

The residual heat is sometimes referred to in the art as the HeatInertia of the auxiliary heater and in the disclosed form the amplitudeof this overshoot is of the order of F., achieving a temporary bimetaldisk temperature as high as 300 F. Thus, even if the energized heatingunit is turned off after a short length of time so that the resistanceelement no longer emits its characteristic orange glow, the indicatorlight 250 will remain energized for a time interval to indicate thatthere is residual heat in the cover plate producing a temperature ofapproximately 120 F. or more. As the thermostatic switch 166 is of thewide temperature differential type, the differential in the present casebeing approximately 50 F the bimetallic disk temperature must fall belowapproximately 120 F. before the disk 247 snaps back to its lower contactposition 240, deenergizing the indicator light 250. This feature isimportant as glass-ceramic has a slow cooling down time because of theproperties of this material.

Again, if either of the radiant heating units 61, 62 remain energizedfor a cooking operation extending for several minutes or longer theconductive heat from the resistance elements 64 or 66 elevates theirassociated heater block to a temperature such that heat flows viaconduction through the metallic bracket channel portions 154, 156 to thebridge plate 158, the porcelain heater 180 and thence to the bimetallicdisk of the thermostatic switch 166. This heat balance arrangement ofthe bracket and heater block renders the bimetallic disk 247 sensitiveto both the energized and residual heat of the heater blocks such thatwhen the cover plate temperature falls below approximately 120 F. thebimetal disk actuation temperature of 120 is also attained to causedeenergization of the indicator light 250.

it will therefore be appreciated that the instant invention provides ananalog of the temperature condition of the cover plate 24 without theuse of expensive high-range-type thermostats to directly sense thetemperature of the cover plate 24 while avoiding any positiveglass-to-metal contact in the heating area directly above the resistanceelement-undesirable because of both the difierential expansion of thetwo materials and because of the obstructing effect upon the directtransmission of infrared rays from the resistance element to the cookingutensil.

While the embodiment of the present invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

I. A presence-of-heat-indicating arrangement for use in combination withan infrared radiant cooking unit having an infrared transmissive coverplate, a resistance element spaced below said cover plate, a fibrousrefractory heater block providing a heat-conductive support for saidresistance element, and a power source for energizing said resistanceelement to radiate heat toward a cooking utensil whereby the temperatureof said infrared transmissive cover plate increases faster than thetemperature of said heater block, said indicating arrangementcomprising; heat-conducting bracket means embedded in thermal contactwith said heater block so as to be in nonradiant heat blocking relationwith said resistance element and said cover plate;temperature-responsive switch means connected to said power source-andin thermal contact with said bracket means; heater means connected tosaid power source for supplying initial heat to said switch means;indicator light means connected to said switch means and exposed to auser of said cooking unit; said switch means serially connecting saidheater means and then said light means to said power source when saidresistance element is energized, said heater means being disconnectedupon energization of said light means and continuing the connection ofsaid light means during the operation of said cooking unit and for apredetermined period after said resistance element is deenergized; saidpredetermined period being controlled by the amount of residual heat ofsaid heater block conductively imparted thereto during the energizationinterval of said resistance element.

2. In an infrared radiant cooking unit the combination of an upperutensil-supporting cover plate of infrared transmissive material, afibrous'ceramic heater block disposed below said cover plate and havinga raised peripheral face defining a central recessed area spaced belowsaid cover plate, means supporting said block with said peripheral faceabutting said cover plate undersurface, resistance element meanssupported on said recessed area in vertically spaced relation below theundersurface of said plate, a circuit for energizing said resistanceelement means across a power source, heat-conducting bracket means inthermal contact with said heater block, said bracket means supportingtemperature-responsive switch means thereon, auxiliary heater meanssupported on said bracket means in heat transfer relation with saidtemperatureresponsive switch means and being in said circuit, indicatormeans in said circuit with said auxiliary heater means, saidtemperature-responsive switch means having terminals connectedalternatively to said auxiliary heater means and said indicator means,said auxiliary heater means being energized whenever said resistanceelement is energized whereby said temperature-responsive switch means isactuated at a first predetermined temperature to initially energize saidindicator means and deenergize said auxiliary heater means, said heaterblock subsequently attaining a temperature level by means of conductiveheat from said resistance element whereby heat will flow from saidheater block through said bracket means to said auxiliary heater means,and said indicator means being deenergized after said resistance elementis deenergized and the residual heat of said cover plate falls below asecond predetermined temperature whereby said temperature responsiveswitch means is actuated to again contact said auxiliary heater meansterminal.

3. The infrared radiant cooking assembly as defined in claim 2 whereinsaid temperature-responsive switch means is a snapaction, bimetal-diskthermostat of the double-pole type.

4. The infrared radiant cooking unit as defined in claim 3 wherein saidthermostat is of the wide differential type calibrated to changeoverduring an ascending heat cycle at approximately 170 F. and to changeoverduring a descending heat cycle at approximately F.

5. The infrared cooking assembly as defined in claim 2, wherein a pairof heater blocks are arranged in spaced side-byside relationship andsaid heat sensitive bracket means disposed therebetween, said bracketmeans formed of metallic sheet material having aligned channel-shapedend portions joined by a central horizontal bracket plate, said endportions extending into opposed conforming cavities in said heaterblocks so as to be in thermal contact therewith, and saidtemperature-responsive switch means being a snap-action, bimetal-diskthermostatic switch positioned in spaced relation with the underside ofsaid bridge plate, and said auxiliary heater means positionedintermediate said thermostatic switch and said bracket plate so as to bein thermal contact with said switch and said plate.

6. The infrared radiant cooking assembly as defined in claim 2, whereinsaid auxiliary heater means is a porcelain-type electric heater having aheat output during its energization phase whereby its thermal inertiawill maintain said temperatureresponsive switch in indicator meansenergization for a time interval sufficient to allow the conductive heatof said heater block to maintain energization of said indicator means.

7. An infrared radiant cooking assembly for a range or the likecomprising an upper utensil-supporting cover plate of infraredtransmissive translucent glass-ceramic material substantially opaque tovisible light rays, a pair of spaced fibrousceramic heater blocksdisposed below said cover plate, each said heater block having a raisedperipheral face defining a central recessed area in spaced relationbelow the undersurface of saidcover plate, means for supporting saidheater blocks with their peripheral faces in abutment with said coverplate undersurface, an infrared-emissive ribbon-shaped resistanceelement located on each said central recessed area in vertically spacedrelation below said cover plate undersurface, each said resistanceelement supported in a continuous convolute-shaped groove so as toextend substantially throughout the full planar extent of its associatedrecessed area, circuit means for energizing said resistance elementsacross a power source, an infinite heat switch in said circuitassociated with each said resistance element for pulsating energizingeach said resistance element to vary the power output therefrom,heatconducting bracket means formed of metallic sheet material disposedin said space between said heater blocks having aligned channel-shapedend portions and a central horizontal bridge plate, said bracket endportions extending into opposed conforming cavities on the underside ofsaid heater blocks such that each end member is in thermal contact withits associated heater block, said bracket supporting a wide-differentialdisk-type thermostatic switch in spaced relation to the underside ofsaid bracket plate, an auxiliary porcelain-type electric heater havingan output of approximately 200 watts at 118 volts supported between saidbracket plate and said thermostatic switch so as to be in heat transferrelation with said bracket plate and said thermostatic switch, saidthermostatic switch being in series electrical circuit with each saidinfinite heat switch, an indicator light in said circuit in parallelwith said auxiliary heater, said thermostatic switch having asinglethrow double-pole switch member providing a first alternateterminal connected to said auxiliary heater and a second alternateterminal connected to a terminal of said indicator light, said auxiliaryheater being initially energized whenever either of said resistanceelements is energized by its associated infinite heat switch wherebysaid thermostatic switch is actuated at a temperature of about F. toenergize said indicator light and deenergize said auxiliary heater, theheat inertia of said auxiliary heater having an overshoot effect toraise the temperature of said thennostatic switch to about 300 F.whereby said indicator light will remain energized until said bracketmeans conducts heat from the heater block associated gized when thetemperature of said thermostatic switch falls below about F. indicatingthat the temperature condition of said cover plate is belowapproximately 120 F.

1. A presence-of-heat-indicating arrangement for use in combination withan infrared radiant cooking unit having an infrared transmissive coverplate, a resistance element spaced below said cover plate, a fibrousrefractory heater block providing a heat-conductive support for saidresistance element, and a power source for energizing said resistanceelement to radiate heat toward a cooking utensil whereby the temperatureof said infrared transmissive cover plate increases faster than thetemperature of said heater block, said indicating arrangementcomprising; heat-conducting bracket means embedded in thermal contactwith said heater block so as to be in nonradiant heat blocking relationwith said resistance element and said cover plate;temperature-responsive switch means connected to said power source andin thermal contact with said bracket means; heater means connected tosaid power source for supplying initial heat to said switch means;indicator light means connected to said switch means and exposed to auser of said cooking unit; said switch means serially connecting saidheater means and then said light means to said power source when saidresistance element is energized, said heater means being disconnectedupon energization of said light means and continuing the connection ofsaid light means during the operation of said cooking unit and for apredetermined period after said resistance element is deenergized; saidpredetermined period being controlled by the amount of residual heat ofsaid heater block conductively imparted thereto during the energizationinterval of said resistance element.
 2. In an infrared radiant cookingunit the combination of an upper utensil-supporting cover plate ofinfrared transmissive material, a fibrous-ceramic heater block disposedbelow said cover plate and having a raised peripheral face defining acentral recessed area spaced below said cover plate, means supportingsaid block with said peripheral face abutting said cover plateundersurface, resistance element means supported on said recessed areain vertically spaced relation below the undersurface of said plate, acircuit for energizing said resistance element means across a powersource, heat-conducting bracket means in thermal contact with saidheater block, said bracket means supporting temperature-responsiveswitch means thereon, auxiliary heater means supported on said bracketmeans in heat transfer relation with said temperature-responsive switchmeans and being in said circuit, indicator means in said circuit withsaid auxiliary heater means, said temperature-responsive switch meanshaving terminals connected alternatively to said auxiliary heater meansand said indicator means, said auxiliary heater means being energizedwhenever said resistance element is energized whereby saidtemperature-responsive switch means is actuated at a first predeterminedtemperature to initially energize said indicator means and deenergizesaid auxiliary heater means, said heater block subsequently attAining atemperature level by means of conductive heat from said resistanceelement whereby heat will flow from said heater block through saidbracket means to said auxiliary heater means, and said indicator meansbeing deenergized after said resistance element is deenergized and theresidual heat of said cover plate falls below a second predeterminedtemperature whereby said temperature responsive switch means is actuatedto again contact said auxiliary heater means terminal.
 3. The infraredradiant cooking assembly as defined in claim 2 wherein saidtemperature-responsive switch means is a snap-action, bimetal-diskthermostat of the double-pole type.
 4. The infrared radiant cooking unitas defined in claim 3 wherein said thermostat is of the widedifferential type calibrated to changeover during an ascending heatcycle at approximately 170* F. and to changeover during a descendingheat cycle at approximately 120* F.
 5. The infrared cooking assembly asdefined in claim 2, wherein a pair of heater blocks are arranged inspaced side-by-side relationship and said heat sensitive bracket meansdisposed therebetween, said bracket means formed of metallic sheetmaterial having aligned channel-shaped end portions joined by a centralhorizontal bracket plate, said end portions extending into opposedconforming cavities in said heater blocks so as to be in thermal contacttherewith, and said temperature-responsive switch means being asnap-action, bimetal-disk thermostatic switch positioned in spacedrelation with the underside of said bridge plate, and said auxiliaryheater means positioned intermediate said thermostatic switch and saidbracket plate so as to be in thermal contact with said switch and saidplate.
 6. The infrared radiant cooking assembly as defined in claim 2,wherein said auxiliary heater means is a porcelain-type electric heaterhaving a heat output during its energization phase whereby its thermalinertia will maintain said temperature-responsive switch in indicatormeans energization for a time interval sufficient to allow theconductive heat of said heater block to maintain energization of saidindicator means.
 7. An infrared radiant cooking assembly for a range orthe like comprising an upper utensil-supporting cover plate of infraredtransmissive translucent glass-ceramic material substantially opaque tovisible light rays, a pair of spaced fibrous-ceramic heater blocksdisposed below said cover plate, each said heater block having a raisedperipheral face defining a central recessed area in spaced relationbelow the undersurface of said cover plate, means for supporting saidheater blocks with their peripheral faces in abutment with said coverplate undersurface, an infrared-emissive ribbon-shaped resistanceelement located on each said central recessed area in vertically spacedrelation below said cover plate undersurface, each said resistanceelement supported in a continuous convolute-shaped groove so as toextend substantially throughout the full planar extent of its associatedrecessed area, circuit means for energizing said resistance elementsacross a power source, an infinite heat switch in said circuitassociated with each said resistance element for pulsating energizingeach said resistance element to vary the power output therefrom,heat-conducting bracket means formed of metallic sheet material disposedin said space between said heater blocks having aligned channel-shapedend portions and a central horizontal bridge plate, said bracket endportions extending into opposed conforming cavities on the underside ofsaid heater blocks such that each end member is in thermal contact withits associated heater block, said bracket supporting a wide-differentialdisk-type thermostatic switch in spaced relation to the underside ofsaid bracket plate, an auxiliary porcelain-type electric heater havingan output of approximately 200 watts at 118 volts supported between saidbracket plate and said thermostatic switch so as to be in heat transferrelation with said bracket plate and said thermostatic switch, saidthermostatic switch being in series electrical circuit with each saidinfinite heat switch, an indicator light in said circuit in parallelwith said auxiliary heater, said thermostatic switch having asingle-throw double-pole switch member providing a first alternateterminal connected to said auxiliary heater and a second alternateterminal connected to a terminal of said indicator light, said auxiliaryheater being initially energized whenever either of said resistanceelements is energized by its associated infinite heat switch wherebysaid thermostatic switch is actuated at a temperature of about 170* F.to energize said indicator light and deenergize said auxiliary heater,the heat inertia of said auxiliary heater having an overshoot effect toraise the temperature of said thermostatic switch to about 300* F.whereby said indicator light will remain energized until said bracketmeans conducts heat from the heater block associated with the energizedresistance element to said thermostatic switch to maintain energizationof said indicator light means whereby said block temperature becomes ananalog of the cover plate temperature, and said indicator light beingdeenergized when the temperature of said thermostatic switch falls belowabout 120* F. indicating that the temperature condition of said coverplate is below approximately 120* F.